Definition: You are given a question on high school psychology. You are also given 4 answer options (associated with "A", "B", "C", "D"), out of which only one is correct. You need to answer the question by selecting the correct option. You should only answer with the choice letter, not the whole answer.
Input: Runners in a park were found to pick up their pace when another runner came into view; this finding illustrates the phenomenon of
(A)social facilitation. (B)conformity. (C)deindividuation. (D)norms.

A